Proceedings of the XLVI Italian Society of Agricultural Genetics - SIGA Annual Congress

Giardini Naxos, Italy - 18/21 September, 2002

ISBN 88-900622-3-1

Poster Abstract - 3.35

Relation between ethylene production and germination ability in tomato (Lycopersicon esculentum Mill.) mutants for genes involved in the hormone perception and synthesis

Lai A.*, Santangelo E.**, Dumitras D.C.***, Giubileo G.*, Fonzo V.**, Soressi G.P.**

*) ENEA, Via E. Fermi 45, 00044 Frascati (RM), ITALY

**) Dept. of Agrobiology and Agrochemistry, Tuscia University, Via S.C. de Lellis s.n.c, 01100 Viterbo, ITALY

***) Dept. of Lasers, National Institute for Laser, Plasma and Radiation Physics, Bucharest, ROMANIA

tomato mutants, germination, ethylene, photoacustic system

Tomato (Lycopersicon esculentum Mill.) is recognised as a useful model plant also for the study of ethylene action. In the last ten years a remarkable progress in the genetic and molecular dissection of the ethylene-response pathway, based on mutants altered in ripening process, has been achieved. The Never ripe (Nr), a mutant for the ethylene receptor Le-ETR3 (Lahan et al., 1994), exhibits a delayed and incomplete fruit maturation. More recently Vrebalov et al. (2002) have evidenced that the ripening inhibitor (rin) mutant, where the ripening is blocked before the respiratory burst, is due to a deletion of a gene belonging to the MADS-box family of transcription factors. A third gene (nor) shows pleiotropic effects similar to rin.

Our work has taken advantage by the availability of i) a photoacoustic laser apparatus, able to detect ethylene production at ppb level; ii) Nr, rin and nor tomato mutants characterized by an alteration in the ethylene pathway. Aim of this study was to analyse the ethylene production during seed germination of the 3 mutants and to correlate it with their germination capacity. Five years old seeds of Nr (in homozygous and heterozygous state), rin, nor (both in homozygous state) and control (cv. NewYorker), were put on Petri dishes and kept at 27°C. Starting when the apical root began to appear (3^th day), the ethylene emission by germinating seeds was measured with a laser based photoacoustic system. The IR laser radiation is emitted by a CW well stabilised CO₂ laser tuned at the 10.532 mm wavelength and modulated by a mechanical chopper at 552 kHz. The modulated laser radiation is focused by a lens (f = 400 mm) through a ZnSe windows into a cylindrical stainless steel resonator containing the gaseous sample. A sensitive microphone (10 mV/Pa) detects the pressure modulation inside the resonator and produces an electric signal proportional to the partial pressure of ethylene, which is fed to a lock-in amplifier synchronised with the chopper. The output signal is transmitted to a PC by an IEEE interface. The observations were performed every day from the third to the seventh (cotyledonary stage) from sowing. In each determination the number of germinated seeds and seedlings at three different stage (with elongating root, with elongating hypocotyls, with visible cotyledons) was recorded.

The three mutants present a higher percentage of germination than the control. Moreover, the results obtained prove that a more prompt and a higher germination are associated with a lower level of ethylene emission. The trend of ethylene production appears different between the control and the mutants. The control shows a progressive decreasing production starting from the third to seventh day; in the nor mutant the ethylene level is more or less constant during germination except at 5^th day; all mutants, but not Nor, show an ethylene increase at 7^th day. By considering the action of the genic products of Nr, rin and nor on ethylene biosynthesis, the data of the present work contribute to elucidate the role of the ethylene on germination ability. The data will be integrated by further analyses on the same mutant seeds of different ages (from 20 to 1 years old), in order to verify the influence of ethylene production on seed vitality and senescence.